1. Field of the Invention
This invention concerns improvements relating to cigarettes and like smoking articles wrapped in paper, hereinafter referred to as cigarettes.
2. Brief Description of the Prior Art
Cigarettes having ventilated areas distributed over the wrapper paper are known. The resultant mixing of air with the smoke not only gives a cooler and milder smoke, but also reduces the delivery of some of the constituents of the smoke.
The delivery of one smoke constituent, carbon monoxide, can be reduced, using a catalyst, by reaction with oxygen to form carbon dioxide. The use of catalysts, particularly in the form of fine particles, presents considerable problems. For example, the catalyst could transfer to the smoke, thereby introducing unwanted, substances, often heavy-metal compounds. Furthermore, catalysts can be deactivated by water adsorption or "poisoned" by smoke constituents.
It is possible to reduce carbon monoxide in cigarette smoke to some extent by using a very porous paper wrapper, but it has been found that the nicotine is also reduced to such a great extent that the cigarette is no longer satisfactory to the smoker. A highly porous paper has also been found to decrease the puff number of the cigarette, which is not desirable. Finally, papers of inherently very high porosity have low breaking strength in the longitudinal direction, which causes problems in cigarette manufacture.
The present invention seeks, in particular, to provide a cigarette capable of giving a smoke with a low ratio of carbon monoxide to nicotine, that is with a substantially normal, acceptable nicotine content, but very low carbon-monoxide content. It is also sought to provide, at the same time, a normal, or greater than normal, number of puffs.